This invention relates to a process for the recovery of metal and insulation in a usable form from an insulated wire scrap. In particular, this invention relates to a process for the selective recovery of specific insulating substances from insulated wire scrap made up of several insulation materials and metal.
Various techniques are common in the art of scrap recovery for removing insulation from insulated wire scrap, but with few exceptions most prior art recovery techniques such as: (1) Mechanical separation, as by abrasion or shearing; (2) Thermal separation, as by incineration of scrap to destroy the insulation, or the use of low temperature to imbrittle the insulation, with subsequent breaking or bending to remove the insulation from the wire; and (3) Chemical stripping of the insulation; and techniques which are primarily directed to the recovery of the conductor metal. Exemplary of the aforementioned techniques are U.S. Pat. Nos. 3,507,427 and 2,956,717, both of which disclose a combination of mechanical and thermal techniques for removing small selected portions of insulation from wire by first cooling the portion of a wire from which the insulation is to be removed to a low temperature and thereafter applying opposed cutting blades to the cooled insulation.
U.S. Pat. No. 3,635,454 is an example of the aforementioned high temperature techniques. Disclosed in U.S. Pat. No. 3,635,454 is a method whereby an organic insulation is subjected to a stream of hot nitrogen gas to affect the depolymerization of the insulation thereby removing the insulation from the conductor.
U.S. Pat. No. 3,666,691, Spiller, discloses a method which departs from the techniques previously discussed. The technique disclosed in Spiller is directed to the recovery of polyvinyl chloride resins from wire scrap by subjecting the resin containing scrap mixture to both the liquid and vapor phases of a solvent mixture in an autoclave and thereafter recovering the vinyl chloride insulation from solution by evaporation.
U.S. Pat. No. 3,624,009, Sussman, discloses a technique whereby polyvinyl chloride resin and fabric material are recovered from fabric material coated with polyvinyl chloride by contacting the coated fabric with a solvent under as inert water-free atmosphere to effectively dissolve polyvinyl chloride and the subsequent recovery of the dissolved polyvinyl chloride from solution by evaporation.
The past practices have almost universally emphasized techniques which either destroy the insulation and recover only the metal conductor or require expensive and time-consuming procedures to separate the various types of scrap to be processed by type of insulating material which is coated upon the conductor scrap. Although each of the aforementioned techniques may be useful for a particular application none of the prior techniques is suitable to be adapted to the continuous selective recovery of high volumes of insulation and metal from wire scrap containing a mixture of insulation materials. Also associated with the aforementioned techniques are numerous problems including: (1) chemical alteration of the insulation being treated which prohibits the reuse of the insulation so treated as a wire insulating material; (2) incorporation into the recovered metal of chemicals which are deleterious to standard metal refining processes; (3) the relatively high cost of the prior techniques; and (4) the production of undesirable pollutants such as smoke, hydrogen chloride, ash and the like which must be disposed of.